Extract variable names from java expression dinamically

Question

I have dynamic set of string expressions(java code parts) eg :

val1.subtract(val2.divide(val3,6,java.math.RoundingMode.HALF_UP) ,new MathContext(6, java.math.RoundingMode.HALF_UP)).setScale(6, BigDecimal.ROUND_HALF_UP)

I want to extract variable names from each expression using java. For above example, output should be:

[val1,val2,val3]

How do I address this issue?

note :

varible names could be any java accepted ones. No any patterns

No specific pattern. They could be anything that java accepts as a variable name — Nilanka Manoj, Aug 04 '21 at 09:10

score 2 · Answer 1 · answered Aug 04 '21 at 09:13

A string which forms a valid java expression requires a complete java parser, capable of parsing every aspect of the entire java language.

This is a valid expression:

new Object() {
    public int test() {
        return 5;
    }
}.test();

Its type is int, and it would evaluate to 5.

You can write anything inside those braces. Including new types.

Thus, there are only two answers available:

Define a restricted set of operations, which means you no longer have 'a java expression', but, a 'NilankaManoj expression'. You'd have to write the spec: Which bits are and are not allowed? Without that spec, your question isn't answerable.
Alternatively, you really do want any java expression, in which case, search the web for an open source java parser. Various parser libraries such as ANTLR 'ship' with a java grammar which is usually out of date and not quite complete. Alternatively, get ecj which is open source. All of these are complex beasts with a very significant learning curve.

Extract variable names from java expression dinamically

1 Answers1